The present invention relates to foams in general, and more particularly, to thermoplastic polymer foams useful in sound management.
In the construction industry, it is well known to use panels as partition walls in order to subdivide the building area into separate areas such as rooms and offices. Usually they consist of an insulating mineral fiber core, and two outer facing layers encompassing the core, and an air gap or hollow space. The insulating materials such as mineral fibers are arranged between the facing layers in such a manner so as to provide thermal and/or acoustic insulation. However, a major disadvantage of such partitions or panels having mineral fiber cores is the lack of mechanical strength of such fibers which therefore require a costly supporting structure or densification. In addition, mineral fiber products are unpleasant to handle causing skin irritation and possibly presenting a health hazard.
Foams have also been utilized as sound insulating materials. For example, WO 95/14136 discloses multilayered insulating panels or elements comprising, in a preferred embodiment, (a) two outer facing layers, and (b) a soft synthetic core material which is a single, continuous, soft, synthetic, closed-cell foam core layer having hollow profiles. The core material is arranged in intimate contact with both outer layers through contact points in alternate patterns, thereby providing gaps between the core layer and the opposing outer layer. However, the closed-cell foam utilized as the core layer in WO 95/14136 provides less than satisfactory sound insulation for demanding applications.
Although not wishing to be bound by any particular theory, the usefulness of a particular polymeric foam in sound management (for example, sound absorption and sound insulation) it is believed by the inventor of the present application to be dependent upon the foam having one or more of the following properties: 1) average cell size greater than about 2 mm; 2) substantially open-cell structure and 3) relatively large pore connecting the cells. In order that the foam be acoustically active, the foam should possess a substantially open-cell structure and a relatively low airflow resistivity. One or more of these same properties also are believed to contribute to the usefulness of a foam for filtering and fluid absorption.
Certain large pore, open-celled foams are known. However, they also possess one or more drawbacks. For example, thermoset resins such as melamine and semi-rigid polyurethane can be used to prepare foams which display the desired large pore, open-celled structure believed to be required for sound management. However, thermoset resins are not recyclable, are costly to manufacture, and are unsuitable for use in humid or wet environments due to their hydrolytic instability. Thermoplastic polymer foams are generally inexpensive to manufacture by a convenient extrusion process, are recyclable, and exhibit hydrolytic stability, and therefore offer an advantage over thermoset resins. However it is difficult to achieve a large-pore thermoplastic foam with an open-cell structure by a convenient direct extrusion process. These difficulties exist because cell opening and foam expansion contradict each other. That is, the growing cells within the foam must remain dosed in order to grow, but developing a large pore requires that a hole must develop on the cell wall shortly before the end of expansion.
In addition, although certain thermoplastic polymer foams are reported to be useful in sound management, it is questionable whether their sound management performance is satisfactory for a demanding application. (See, for example, DE 3,626,349 to Dynamit Nobel A G, published Feb. 11, 1988, DE 3,626,350 to Dynamit Nobel A G, published Feb. 11, 1988, and WO 95/14136, to Dow Chemical, published May 26, 1995).
Therefore, there remains a need in the art for foams which provide sound deadening properties satisfactory for demanding applications, which have mechanical strength, which are economical to manufacture, and which are hydrolytically stable.
That need is met by the present invention. Thus, the present invention provides thermoplastic polymer foams having sound deadening properties satisfactory for demanding applications, which have mechanical strength, which are economical to manufacture, and which are hydrolytically stable.
Thus, in one embodiment of the present invention, there is provided thermoplastic polymer foams having an average cell size greater than about 4 mm are provided.
In another embodiment, there is provided thermoplastic polymer foams having an average cell size of greater than about 2 mm wherein greater than about 50 percent of the cells have been opened by mechanical means are provided.
In yet another embodiment, the present invention provides a thermoplastic polymer foam having an airflow resistivity of less than about 800,000 Rayls/m and an average cell size of greater than about 2 mm, and wherein greater than about 50 percent of the cells have been opened by mechanical means.
In yet still another embodiment, the present invention provides processes for preparing thermoplastic polymer foam structures having an average cell size of greater than about 2 mm, and wherein greater than about 50 percent of the cells have been opened by mechanical means.
The foams of the present invention are particularly useful for sound absorption, sound insulation, fluid absorption, filtering, cushion packaging and other applications requiring one or more of the following properties: sound deadening or sound damping properties, mechanical strength, economical manufacture, and hydrolytically stability.